1. Field of the Invention:
This invention relates to a sheet metal poly-V pulley having poly-V grooves formed at specified pitches in the peripheral wall of a cup-shaped blank, and a manufacturing method thereof.
2. Prior Art:
Conventionally, sheet metal poly-V pulleys of this type, that is, sheet metal made poly-V pulleys having a plurality of V-grooves, or so-called poly-V grooves, formed at specified pitches on the peripheral wall of a cup-shaped blank possessing bottom wall and peripheral wall formed by deep drawing of sheet metal blank, have been merchandized, and used widely as intermediate conduction poly-V pulleys in, for example, vehicles engine appliances.
Incidentally, this kind of sheet metal poly-V pulley, unlike the cast product, is very light in weight because a thin sheet metal blank is drawn, rolled and processed, and the rotation transmission efficiency to the belt to wind around is very high, so that the rotation may be properly transmitted to the belt if rotated at high speed. Aside from such advantages, more recently, the strength of the poly-V belt to be wound around the sheet metal poly-V pulley is extremely improved, and thanks to the enhancement of strength of this poly-V belt, the poly-V belt is not broken if the sheet metal poly-V pulley is rotated at a considerably high speed. That is, in order to rotate the poly-V belt at high speed, it must be wound around and engaged with the sheet metal poly-V pulley at a very high tension, and if rotated by winding and engaging at such high tension, the poly-V belt is not broken in the present situation.
However, as stated above, when rotated in engagement by winding the poly-V belt around the sheet metal poly-V pulley at high tension, since the poly-V pulley is made of a thin sheet metal blank, plastic deformation is likely to occur in the peripheral wall and bottom wall, or crossing parts of bottom wall and peripheral wall, and it is sometimes difficult to strengthen the pulleys as the strength of poly-V belts increases.
In this case, to prevent deformation of the sheet metal poly-V pulley, it may be possible to cope with the enhancement of strength of poly-V belt by using a considerably thick sheet metal blank, but it may result in a large increase in the material cost or difficulty in forming to manufacture a sheet metal poly-V pulley from a thick sheet metal blank, and also increase in the weight, which may finally sacrifice the advantages of the sheet metal poly-V pulley.